1. Field of the Invention
The present invention relates generally to continuous casting of molten metal, and more particularly to an apparatus for manual interruption of molten metal flow from a metering orifice.
2. Discussion of the Prior Art
The continuous casting of metals frequently involves four distinct steps. First, metal stock, often at ambient temperature, is placed in a furnace, wherein sufficient heat is applied to reduce the metal stock to a liquid state in which the metal may be poured. Second, a suitable means of conveyance, in most cases a ladle or bucket adapted for the purpose and attached to an appropriate structure for free movement about the work space, is lowered into or adjacent the furnace where it is filled with molten metal by dipping or pouring. Third, the ladle or bucket is conveyed to a tundish, where the molten metal is poured into the tundish. Finally, the tundish ordinarily includes one or more metering nozzles or orifices on its underside, and these are positioned above one or more molds so that the molten metal may pass freely from the nozzle into the mold.
In normal operation, this procedure is not particularly hazardous. However, in the event of a power failure, a potentially dangerous situation may be presented. In such a circumstance, it is quite likely that the mold will cease drawing material, so that as the molten metal continues to flow through the nozzles, the mold will fill to capacity in a short period of time. When the mold is thus filled, and molten metal continues to flow from the tundish, such excess molten metal will flow onto the floor of the work space, presenting a danger to workers and equipment.
In view of this potentially dangerous situation, it has long been recognized that a method for interrupting the flow of molten metal during an emergency is necessary. In the past, at least three common methods for interrupting molten metal flow have been used. The most primitive of these methods has been the use of an L-shaped steel bar, with a chill plug of appropriate dimension attached to the end of the short leg. In this method, an operator simply uses the long leg of the steel bar as a handle, and inserts the chill plug into the orifice. The operator must then hold the steel bar in this position until the metal in the orifice solidifies, normally a period of between 20 and 30 seconds.
A second method or system for addressing the problem has been to provide what is known as a "slide-gate" mechanism. The "slide-gate" mechanism is a valve system of which the nozzle is a part. As the name implies, in this system a sliding plate valve incorporated with the nozzle is used to seal the tundish orifice in the event of an emergency. Closure of the "slide-gate" generally takes 4-5 seconds. Finally, the interruption system set forth in Remeika U.S. Pat. No. 4,461,336 provides an apparatus that is normally automated and which incorporates a piston driven linkage system for inserting a chill plug into a tundish nozzle.
The existing methods for interrupting the flow of molten metal during an emergency have various shortcomings. Obviously, the manual system of using an L-shaped steel bar to insert a chill plug presents a very dangerous situation to the operator. In this manual system, the operator must stay in close proximity to the tundish and hold the L-shaped steel bar in place, usually for from 20 to 30 seconds, until sufficient hardening occurs to block flow from the orifice. While he is doing this, molten metal may continue to flow from adjacent orifices, splashing onto the work place floor, as well as on the operator himself. However, since the operator cannot leave the first nozzle until it is sealed, the dangerous flow of molten metal from other nozzles simply must continue until he is free to move, or until other operators become available.
While the "slide-gate" method is somewhat more safe from the point of view of the operator, this system is also more expensive since the sliding valve is incorporated with the nozzle, and the entire nozzle slide-gate is rendered unusable once it has been used in an emergency situation. The nozzle-slide gate costs approximately $250.00 per individual nozzle, and each must be replaced after use. In addition, the entire assembly is priced in the region of $10,000.00 per unit.
Finally, the more sophisticated system disclosed in U.S. Pat. No. 4,461,336 can present several difficulties. When the system disclosed in the patent is operated in the automated mode, it reduces the control that the operator must have during an emergency situation. For example, the patent does not disclose that the linkage arm controlling the chill plug may be adjusted for optimum engagement of the plug with the orifice. This is of critical importance because in most continuous casting applications, the tundish nozzle is replaced after each use. When such nozzles are replaced, there is quite often considerable "play" in the newly fitted nozzle, so that a flow interrupter plug that is not adjustable will not always properly seat within the nozzle. This problem is addressed in the present invention, which provides a flow interrupter plug that is adjustable.
Further, in many applications a protective shroud, often called a "Pollard shroud", is used to control potential splashing of molten metal as it exits the nozzles. This is a tin shroud placed around the stream of liquid steel, into which is fed gaseous nitrogen to prevent oxidation. This protective shroud is not conducive to the use of the patented device, which requires more space than is available when the shroud is used. In addition, the Remeika device is permanently mounted on the tundish. This not only affects the relationship of the flow interrupter plug to the nozzle, as noted above, but also reduces the flexibility of the entire system.